This invention relates generally to printers useful for producing hard copy output of electronically represented data supplied, for example, from the central processor unit of a computer system. More particularly, the invention relates to improvements in such printers so as to enable them to selectively print in multiple colors.
The prior art is replete with various printer systems, all suitable for printing text material, comprised of alphanumeric characters, in response to electronically digitally represented data supplied thereto. Moreover, in recent years, printer systems have been developed which are not only capable of printing alphanumeric characters, but which are also capable of plotting (which term herein after shall generally refer to producing hard copy output of arbitrary patterns). One such class of mechanisms which has gained wide acceptance in recent years is known as a "dot matrix impact" printer/plotter. Such devices are capable of selectively operating in either a print mode or a plot mode. A typical dot matrix impact unit is disclosed in U.S. Pat. No. 3,941,051 which is believed to essentially describe a commercially available product marketed by Printronix, Inc., Irvine, California, as the model P300 printer. Similar units are available from other manufacturers and are variously described in the literature.
In a typical dot matrix impact printer, a hammer bank carrying a plurality of individually actuatable hammers is mounted for reciprocating movement along a print line. Each hammer is capable of printing a single dot in each position of the hammer bank but since the bank is mounted for movement along the print line, each hammer can print multiple dots along the line. For example, a typical dot matrix impact printer may use a forty-four hammer bank capable of printing a one hundred thirty two column (character) wide page with each hammer being capable of laying down thirty dots for a total of 1,320 dots across the print line. After each dot line is printed, the paper is moved incrementally and then the next dot line is printed. In high quality dot matrix impact printers, adjacent dots can be overlapped to allow solid lines or areas to be printed. For example, the diameter of each dot can equal 0.020 inches and the center-to-center spacing between dots, both horizontally and vertically can be 0.010 inches. As a consequence of the foregoing, arbitrary dot patterns can be layed down under the control of the input data. Printing or plotting in accordance with the foregoing has typically been performed in only a single color.